how do you use a roofing square

Hi all newbie here i was wondering how do you use a roofing square and it's convertion tables,i feel a bit embarrased as i did C+J for two years at college but i never moved on to roofing,any help guides or links would be great,because it baffles me?
Thanks

Being a red-faced 'Newbie' meself, and not being a roofer, I would let one of the real 'red back's' tell you how to use one, but (very briefly) they work roughly as follows :

To set out a roof, the rise of the roof is set on the narrow bit (the tongue) and the run of the rafter is set on the the wider bit (the blade), you'd then normally set the rise and run on the square by scaling down your measurements by ten. E.g. 3.5m becomes 350mm and so on. You join the readings on both scales using a batten or the like, and you get your various required lengths and angles from these readings.

The tables that are often on them give rafter lengths per metre run for 'standard' pitches.

That's as much as I know about roofing squares ! Over to one of the Pro's !